The acts that, to be perfected, must be wholly devoted to G-d when they are performed are the acts of worship, through which we hope to attain G-d’s favor, namely, all the observable duties, performed with the limbs. In these, one’s aim in doing them might be something other than for the sake of G-d. One’s aim might be to adorn himself with them before other people, and to be honored and praised by people for having performed them.

It is impossible, however, to curry favor or gain honor and praise by fulfilling any of the duties the heart, because people do not know what is in one’s heart. Rather, one intends them for the sake of the One Who observes, namely, the Creator, alone, as it says: “I, G-d, search the heart and test the mind” (Yirmiyahu 17:10); “The hidden things belong to HaShem our G-d” (Devarim 29:28).